
I previously wrote about knowing the enemy: Know the enemy
But that isn't enough to reliably win a fight. As Sun Tzu said, knowing yourself is also critical.
When was the last time you cleaned your carry gun? Last time you did a function check? Last time you drew your carry pistol from your carry holster from actual street concealment? Last time you did it under time pressure? Under physical stress? Last time you shot your carry pistol at 3-to-7 yards?
This is a diagram of the Preparedness cycle:

The preparedness cycle is the process emergency management professionals use to make sure that when the moment of truth arrives, they are ready.
Many people have a plan or purchase a firearm for self defense... but too few actually train or do realistic rehearsals. Since they don't train enough or do realistic rehearsals they never discover problems with their plan or equipment and never do an evaluation or realize they need to improve undiscovered deficiencies.
Shooting a lot, I see people with pistols that don't function, are not properly cleaned and lubricated, with bad ammo. They practice with range guns/ammo/holsters/concealment, but not what they carry for self defense. Half the work my gunsmith does is restoring firearms that were improperly maintained and rusted out. These problems are common.
If you don't train and do realistic rehearsals you may not discover a major problem until the moment of truth arrives... and then it's too late.
Success is following Sun Tzu's timeless advice. Know yourself AND the enemy